This invention relates to devices which reduce the aerodynamic drag of motorized road vehicles such as articulated and nonarticulated trucks. This invention more specifically relates to devices which reduce truck drag by altering the external geometry of the truck afterbody.
It is well known that the large blunt base area typically found in the trailing edge region of a truck body/trailer box is a major source of aerodynamic drag. The airflow in the region behind the flat blunt base trailing edge is almost always completely separated, and typically base pressure coefficients are found to be of the order of -0.2 (see for example Reference 1). To improve this situation, add-on trailing edge fairings which have streamlined tapering surfaces have been proposed in the prior art. These devices, sometimes inflatable (for example McDonald, U.S. Pat. No. 4,006,932), can reduce the equivalent aerodynamic blunt base area of the truck body on which they are installed. However, the use of these devices entails several disadvantages. Perhaps most importantly, many trucks already have lengths at the legal limits, and the use of long trailing edge streamline fairings on already long trucks would further compound existing safety and traffic problems on the highways. Another disadvantage of existing fairing devices is that they are difficult to stow away when not in use. These devices are also likely to block or interfere with the operation of rear loading door(s) on the truck body. Finally, the existing devices may also involve significant weight and initial cost penalties.